This invention relates to treatment of water by reverse osmosis. Osmosis is the natural tendency for a dilute liquid to pass through a semipermeable membrane to a more concentrated liquid. Reverse osmosis requires high pressure on the sea water, for example, so that clear water will pass through the semi-permeable membrane and be recovered while leaving the salt ions and other impurities behind. Reverse osmosis is used to treat salt water and brackish water to deliver a product relatively free of salt and other contaminants. The process is used to treat potable water to deliver a product which has greater purity...in some cases the process is applied in series to end up with very pure or laboratory quality water. Impurities are removed on each pass through the membrane. The process is used on gases. Ships and boats use the process to produce potable water and reduce the amount which has to be stored in tanks. Many shore installations are required because the wells are brackish or sea water has to be treated.
In view of differing types of fluids (i.e., liquid or gas) which are treated by reverse osmosis, the input will be referred to as "untreated fluid" (which contains impurities) and the useable output (clear water, etc.) is referred to as "product" [which impurities (not all impurities, however) have been removed] while the fluid which is returned to the source is referred to as "waste" or "waste fluid". If more impurities are to be removed, the "product" is passed through another reverse osmosis treatment.
A conventional reverse osmosis system draws in untreated fluid, passes it through a filter(s) and then a high pressure pump injects the fluid into the reverse osmosis vessel where the product passes through the membranes for recovery while the waste fluid is returned to the source. The high pressure pump maintains the pressure at 800 psi when treating salt water. The waste coming out of the reverse osmosis vessel is close to atmospheric pressure. Typically, the product recovery is 10% of the sea water pumped. Thus, for every 100 gallons of product, the high pressure pump must handle 1,000 gallons of sea water at 800 psi. High pressure and high volume translates to high cost.
Reverse osmosis systems are typically used in areas where the cost of electric power is very high or must be generated. On a boat the cost of a generator is appreciable and space is at a premium.